<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>画三角形</title>
    <style>
        #trip{
            width: 0px;
            height: 0px;
            border-top:500px solid white;
            border-right:500px solid white;
            border-bottom: 500px solid yellow;
            border-left: 500px solid white;
        }
    </style>
</head>
<body>
<div id="trip"></div>
</body>
</html>